Marine propellers have traditionally been made in a one piece casting process. In such a process, a metal alloy selected for its strength, as well as its desired combination of erosion and corrosion resistant properties, is poured into a mold and cast into the generally desired shape for the propeller. The casting is then machined to the desired final shape.
More recently, some marine propellers have been produced by joining a propeller hub and a plurality of propeller blade blanks. The blade portions each have an inner attachment portion suitable for attachment to the hub. Typically in such a process, the identical blade portions are separately cast, and later each is welded or brazed into position around the hub.
With respect to high speed propellers of the type that is of interest to us, the problem with such heretofore used casting processes known to us is that the propellers must have relatively thick blade profiles to ensure adequate strength. Consequently, an undesirable amount of motor horsepower is consumed in simply driving the propeller through the water.
One attempt to improve on such prior art propellers and their production methods is set forth in U.S. Pat. No. 4,555,835 issued on Dec. 3, 1985 to to Buzzi et al for PROCESS FOR PRODUCING PROPELLERS. Buzzi provides for a propeller blade and a corresponding segment of a propeller hub to be press forged. The linear mating surfaces which are provided parallel the driving shaft along the hub portion of the propeller segments are then beveled. The propeller segments are subsequently joined using filler weldment in a generally V-groove shaped joint which is formed linearly along the hub from front to rear thereof.
Although Buzzi discloses a process that results in an increase in individual propeller blade strength, we have found that improvements in hub strength are still desirable. Also, a reduction in the size of the heat affected welding zone would be desirable in order to reduce the potential for propeller blade failure by fatigue stress along the welded portions of the hub.